Last Updated: 12:01am GMT 09/03/2008

Bee Wilson looks into the murky world of olive oil

'Extra-virgin' suggests great purity. It sounds even better in Italy, land of superlatives and Madonnas: extravergine. It rolls off the tongue like a prayer. So it's a shame that much Italian extra-virgin olive oil - perfect oil from the first pressing of olives - is anything but.

Adulterated olive oil is now the biggest agricultural fraud in the EU. Some 'extra-virgin Italian olive oil' is actually shipped in from Tunisia or Libya. Other times, fraudsters will take bog-standard cooking olive oil (or even lamp-grade oil not legally designated for human consumption) and dose it with green chlorophyll to make it look suitably virginal. In January Italy brought in a law to stop the fraud - from now on olive-oil producers are obliged to state on the label where the olives were grown and pressed. Few believe this will change anything. The incentives for fraud are too great. As one oil-law enforcer told the New Yorker last year, 'Profits were comparable to cocaine trafficking, with none of the risks.'

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The rising black market in Italian extra-virgin is a sign of the world's unstoppable love affair with the green stuff. In 2006 sales of extra-virgin olive oil in Britain reached £71 million. Some buy it for health - the mono-unsaturated fat and polyphenols believed to help our hearts. Some buy it for taste - the peppery tang of a Tuscan oil, the almondy freshness of a Ligurian. But more, I suspect, buy it for a little whiff of sophistication.

But do we really know what to do with it? Gillian Riley is a scholar and connoisseur of the food of Italy who has distilled all of her years of knowledge into The Oxford Companion to Italian Food. It is a delightful, erudite book. You pick it up meaning to look up just one thing - panna cotta, say- and find yourself still transfixed an hour later. Riley is unimpressed by the British fetish for Italian olive oil.

One thing that annoys Riley is the use of the word 'drizzle'. 'Drizzle is a noun with a precise meteorological meaning - "a fine misty rain" - and when used as a verb it means "to shed or let fall in minute drops or particles". Not an accurate way to describe pouring moderate amounts of olive oil over food.' Nor is Riley impressed by the 'weird custom of putting a saucer of oil on the table to dip bread in at the start of the meal'. She calls this 'pretentious', a 'foreign aberration' that you never see in Italy, where they eat their bread plain.

More generally, Riley thinks that we vastly overuse extra-virgin. 'Frying with an oil of quality is a wanton waste of a precious commodity, like freshening the kitchen sink with Chanel No 5.' An Italian cook will think carefully whether to start a dish with olive oil - the ordinary virgin kind is fine - butter or lard. Expensive extra-virgin should be saved to use as a condiment, the better to appreciate its powerful aromas. Riley suggests pouring it - not drizzling! - over lukewarm asparagus, artichokes, and fresh young peas and beans; using it to 'anoint' crostini; or adding it to vegetable stews and soups for a 'last-minute charge of flavour'. If we bought less - and better - oil, then maybe 'extra-virgin' would actually mean something again.

'Swindled: From Poison Sweets to Counterfeit Coffee - The Dark History of the Food Cheats' (John Murray, £14.99) by Bee Wilson is out now